The controversy involves questions about when wastewater is subject to Clean Water Act permitting requirements.

The process a Hawaii county uses to dispose of treated sewage by pumping it underground, where at least some if it flows to the ocean, has led to a legal dispute over the scope of a federal environmental law that the U.S. Supreme Court on Tuesday agreed to consider.

State leaders and groups representing water and sewer agencies, cities and counties say that if the high court lets a federal appeals court ruling stand in County of Maui v. Hawaii Wildlife Fund, et al., it could greatly expand the reach of the Clean Water Act.

This, they warned, will result in new costs, added bureaucratic burdens and other complications for states and local governments.

The environmental organizations that brought the case against the county have raised doubts about the extent to which that would be so, saying that Maui County’s claims that the 9th U.S. Circuit Court of Appeals decision would sweep millions of new sources into a Clean Water Act permit program are “alarmist.”

They also say the way the county has disposed of the sewage has had devastating effects on a once-pristine coral reef off Hawaii’s coast.

The controversy in the case stems from the operation of the Lahaina Wastewater Reclamation Facility, which was designed in the 1970s and is owned and operated by the county. The facility processes about four million gallons of sewage per day, according to court filings.

Treated waste from the plant is injected underground via four wells, where it mixes with groundwater. An Environmental Protection Agency study has shown that some of the wastewater later flows from underwater seeps in the Pacific Ocean.

The environmental groups cite estimates indicating that the wastewater makes up about one out of every seven gallons of groundwater entering the ocean near the facility.

Enacted in 1972, the Clean Water Act is one of the nation’s bedrock environmental laws. It prohibits the discharge of pollutants into “navigable waters” from a “point source”—unless the discharge has been authorized by the permitting requirements outlined in the act.

A classic example of a “point source” in the context of the law would be pipe that empties a contaminant of some sort into a waterway or the ocean. Other possibilities could include ditches, tunnels, rail cars, or ships that are used to empty pollutants into water.

In the Maui case, the controversy is over whether contaminants discharged from a point source—in this case the wells—that flow through groundwater and eventually end up in navigable waters, are subject to the Clean Water Act.

Maui County argues that the groundwater at issue in the case falls into the category of “nonpoint” source pollution that is not subject to the law's National Pollutant Discharge Elimination System permitting, but is subject to other state and federal regulations.

The 9th Circuit, however, sided against the county, ruling that the pollutants reaching the Pacific from the Lahaina facility are “fairly traceable from the point source to a navigable water.” And the court said the contaminants exceeded the “de minimis” threshold for triggering the Clean Water Act permitting requirements.

“At bottom, this case is about preventing the County from doing indirectly that which it cannot do directly,” the court's ruling says.

It goes on to note that the county could not, under the Clean Water Act, dump pollutants directly into the ocean without the proper permit. “It cannot do so indirectly either to avoid CWA liability,” the ruling adds. “To hold otherwise would make a mockery of the CWA’s prohibitions.”

The county in its petition says that the 9th Circuit created a “new test” for National Pollutant Discharge Elimination System permitting based on the “traceability and volume” of pollutants reaching water.

But the county says the court did not clarify when, if ever, the connection between a point source and a body of water “is too tenuous to support liability under the CWA.”

Eighteen attorneys general, all but one Republican, and the GOP governors of Kentucky and Mississippi filed a brief last October in support of Maui County.

They say the appeals court ruling in the Maui case—along with a similar 4th Circuit ruling in a case involving a pipeline that ruptured and spilled thousands of gallons of gasoline in South Carolina—will upset a balance between states and the federal government when it comes to environmental regulation.

The 9th Circuit decision, the brief from the state officials says, tips that balance toward the federal government and “infringes on the sovereign prerogative” of states to manage their waters.

Their brief also points out that most states have taken on primary responsibility over Clean Water Act permitting and that expanding the scope of the law would also create new work and costs for states.

They say municipalities and other entities around the U.S. use over 650,000 injection wells in the process of purifying and recycling wastewater, while oil and gas producers use around another 180,000.

The officials raise the possibility that even home septic systems could require Clean Water Act permitting based on the 9th Circuit’s standard.

The National League of Cities, the National Association of Counties, the National Water Resources Association and other water, wastewater and municipal organizations around the U.S. also filed a brief with the Supreme Court in support of Maui County.

“The situation in Maui is not unique,” their brief says.

The Trump administration urged the Supreme Court to weigh in on the Maui County case. Solicitor General Noel Francisco’s office noted that the 9th Circuit ruling, along with the 4th Circuit decision in the gasoline pipeline case, conflict with a pair of 6th Circuit rulings in cases over alleged pollution from coal ash waste.

The Maui case is likely to be heard by the justices in the fall.

Bill Lucia is a Senior Reporter for Route Fifty and is based in Olympia, Washington.